Channel access mechanism

ABSTRACT

A method and system to improve backoff counter handling with relation to a clear channel assessment (CCA) process. The method and system improve a wireless medium availability by adjusting the backoff counter such that the processing of a preamble of a frame received during a backoff is taken into account. Received frames that fall between two CCA thresholds may require decoding of information in the preamble to assess whether the wireless medium is available. A portion of the preamble is decoded that identifies information utilized to determine whether the wireless medium may be considered to be busy. However, during this determination that requires the reading of the preamble of a received frame the backoff counter may be held or decremented even though the wireless medium status is unknown. The method and system provide a set of possible adjustments to the backoff counter to account for this uncertainty and the outcome of the CCA.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/083,138, filed Nov. 21, 2014, and U.S. Provisional Application No.62/157,357, filed May 5, 2015, which are hereby incorporated byreference.

FIELD OF INVENTION

The embodiments of the invention are related to the field of wirelesslocal area network (WLAN) operation. More specifically, the embodimentsof the invention relate to a method and system for improving theefficiency in assessing the availability of the wireless medium byimproving the backoff mechanism in the clear channel access (CCA)process. Other embodiments are also disclosed.

BACKGROUND

Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a setof physical and media access control (MAC) specifications forimplementing wireless local area network (WLAN) communications between aset of network devices, referred to as stations, and/or access points.These specifications provide the basis for wireless network productsusing the Wi-Fi brand managed and defined by the Wi-Fi Alliance. Thespecifications define the use of the 2.400-2.500 GHz as well as the4.915-5.825 GHz bands. These spectrum bands are commonly referred to asthe 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channelswith a center frequency and bandwidth. The 2.4 GHz band is divided into14 channels spaced 5 MHz apart, though some countries regulate theavailability of these channels. The 5 GHz band is more heavily regulatedthan the 2.4 GHz band and the spacing of channels varies across thespectrum with a minimum of a 5 MHz spacing dependent on the regulationsof the respective country or territory.

Communication, on any given channel of either the 2.4 GHz or the 5 GHzband, between network elements of the WLAN utilizes the clear channelassessment (CCA) protocol. CCA is defined in the IEEE 802.11 standard aspart of the Physical Medium Dependent (PMD) and Physical LayerConvergence Protocol (PLCP) layer. Clear Channel Assessment is composedof two related functions, carrier sense (CS) and energy detection (ED).The CCA protocol is implemented in the physical layer (PHY) of a networkdevice and determines the current state of use of the wireless medium(WM) (i.e., a 2.4 GHz or 5 GHz band), such that a network device (e.g.,a station) will access a channel of the WM only when the WM becomesidle.

The conventional CCA rule mechanism defined in IEEE 802.11 defines theprimary channel to be busy, if one of the conditions listed in the TableI is met, otherwise the primary channel is considered to be idle. If theprimary channel is idle, the PHY will check the secondary channels.

TABLE I Operating Channel Width Conditions 20 MHz, 40 MHz, 80 MHz, Thestart of a 20 MHz NON_HT PPDU in the 160 MHz or 80 + 80 MHz primary 20MHz channel as defined in 18.3.10.6 (CCA requirements) 40 MHz, 80 MHz,160 MHz The start of a 40 MHz non-HT duplicate or or 80 + 80 MHz VHTPPDU in the primary 40 MHz channel at or above −79 dBm, The start of anHT PPDU under the conditions defined in 20.3.21.5 (CCA sensitivity) 80MHz, 160 MHz or The start of an 80 MHz non-HT duplicate or 80 + 80 MHzVHT PPDU in the primary 80 MHz channel at or above −76 dBm 60 MHz or80 + 80 MHz The start of a 160 MHz or 80 + 80 MHz non- HT duplicate orVHT PPDU at or above −73 dBm

SUMMARY

The embodiments provide a method and system for wireless mediumimproving backoff counter handling with relation to a clear channelassessment (CCA) process. The method and system improve a wirelessmedium availability by adjusting the backoff counter such that theprocessing of a preamble of a frame received during a backoff is takeninto account. The method and system adjust the backoff counter to avoidit being unnecessarily held which delays the transmission of the networkdevice on the wireless medium. In some embodiments, a check is madewhether a frame received during a backoff period has a signal qualitylevel below a first threshold level. If the received frame has a signalquality level below the first CCA threshold level then a check is madewhether the received frame is above a below a second CCA thresholdlevel. Received frames that fall between these two CCA thresholds mayrequire decoding of information in the preamble to assess whether thewireless medium is available. A portion of the preamble is decoded thatidentifies information utilized to determine whether the wireless mediummay be considered to be busy. However, during this determination thatrequires the reading of the preamble of a received frame, the backoffcounter may be held or decremented even though the wireless mediumstatus is unknown. The embodiments provide a set of possible adjustmentsto the backoff counter to account for this uncertainty and the outcomeof the CCA.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that differentreferences to “an” or “one” embodiment in this specification are notnecessarily to the same embodiment, and such references mean at leastone. Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

FIG. 1 is a flowchart of one embodiment of a process for adjusting abackoff counter as part of the CCA process.

FIG. 2 is a diagram illustrating a standard CCA process including abackoff counter process.

FIG. 3A is a diagram illustrating a first case of a first embodiment ofan alternate backoff counter process.

FIG. 3B is a diagram illustrating a second case of the first embodimentof an alternate backoff counter process.

FIG. 4A is a diagram illustrating a first case of a second embodiment ofan alternate backoff counter process.

FIG. 4B is a diagram illustrating a second case of the second embodimentof an alternate backoff counter process.

FIG. 5A is a diagram illustrating a first case of a third embodiment ofan alternate backoff counter process.

FIG. 5B is a diagram illustrating a second case of the third embodimentof an alternate backoff counter process.

FIG. 6A is a diagram illustrating a first case of a fourth embodiment ofan alternate backoff counter process.

FIG. 6B is a diagram illustrating a second case of the fourth embodimentof an alternate backoff counter process.

FIG. 7 is a diagram of one embodiment of a network device implementingthe adjusted backoff counter process.

FIG. 8 is a schematic block diagram exemplifying a transmitting signalprocessor in a WLAN device.

FIG. 9 is a schematic block diagram exemplifying a receiving signalprocessing unit in the WLAN.

FIG. 10 is a diagram of an example wireless local area network.

FIG. 11 is a timing diagram providing an example of the carrier sensemultiple access/collision avoidance (CSMA/CA) transmission procedure.

FIG. 12 is a diagram of a very high throughput (VHT) physical layerconvergence protocol (PLCP) protocol data unit PPDU utilized by a WLANdevice physical layer.

FIG. 13 is a table of the fields of the VHT PPDU.

DETAILED DESCRIPTION

The embodiments provide a method and system for wireless mediumassessment for a network device in a wireless communication system suchas a wireless local area network (WLAN) implementing IEEE 802.11. Themethod includes a method of adjusting a backoff counter to take intoaccount increasingly complex clear channel assessment (CCA) processesthat involve dynamic CCA thresholds or similar changes that increase theavailability of a wireless medium. The method improves wireless mediumavailability by adjusting the backoff counter to account for processingof a preamble of a received frame to determine whether the wirelessmedium is available. With the embodiments, the backoff counter is notunnecessarily held which delays the transmission of the network deviceon the wireless medium. In some embodiments, a check is made whether aframe received during a backoff period has a signal quality level abovea CCA first threshold level. If the received frames have a signalquality level above the first CCA threshold level then a check is madewhether the received frame is above or below a second CCA thresholdlevel, where the second CCA threshold level is higher than the first CCAthreshold level. The first CCA threshold level and second thresholdlevel can be checked in sequence or parallel. Received frames that fallbetween these two CCA thresholds may require decoding of information inthe preamble to assess whether the wireless medium is available. Forexample, a portion of the preamble that identifies a basic services set(BSS) of the transmitting network device may be examined to determinewhether the transmitting network device is in the same BSS as theimplementing network device. In which case, the wireless medium may beconsidered to be busy. However, during this determination that requiresthe reading of the preamble of a received frame the backoff counter isheld even though the wireless medium may be considered by the CCAprocess to be idle. As a result, the implementing network device ismissing an opportunity to make use of the wireless medium in a timelymanner. The embodiments overcome these disadvantages of the art byadjusting the backoff counter in certain situations. This adaptabilityin the use of the backoff counter in turn increases the availability ofthe wireless medium and thereby the throughput of the wirelesscommunication system.

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description. It will beappreciated, however, by one skilled in the art that the invention maybe practiced without such specific details. Those of ordinary skill inthe art, with the included descriptions, will be able to implementappropriate functionality without undue experimentation.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.“Coupled” is used to indicate that two or more elements, which may ormay not be in direct physical or electrical contact with each other,co-operate or interact with each other. “Connected” is used to indicatethe establishment of communication between two or more elements that arecoupled with each other. A “set,” as used herein refers to any positivewhole number of items including one item.

The operations in the flow diagrams will be described with reference tothe exemplary embodiments of the other figures. However, it should beunderstood that the operations of the flow diagrams can be performed byembodiments of the invention other than those discussed with referenceto the other figures, and the embodiments of the invention discussedwith reference to these other figures can perform operations differentthan those discussed with reference to the flow diagrams.

An electronic device stores and transmits (internally and/or with otherelectronic devices over a network) code (which is composed of softwareinstructions and which is sometimes referred to as computer program codeor a computer program) and/or data using machine-readable media (alsocalled computer-readable media), such as non-transitory machine-readablemedia (e.g., machine-readable storage media such as magnetic disks,optical disks, read only memory, flash memory devices, phase changememory) and transitory machine-readable transmission media (also calleda carrier) (e.g., electrical, optical, radio, acoustical or other formof propagated signals—such as carrier waves, infrared signals). Thus, anelectronic device (e.g., a computer) includes hardware and software,such as a set of one or more processors coupled to one or morenon-transitory machine-readable storage media (to store code forexecution on the set of processors and data) and a set of one or morephysical network interface(s) to establish network connections (totransmit code and/or data using propagating signals). Put another way, atypical electronic device includes memory comprising non-volatile memory(containing code regardless of whether the electronic device is on oroff) and volatile memory (e.g., dynamic random access memory (DRAM),static random access memory (SRAM)), and while the electronic device isturned on that part of the code that is currently being executed iscopied from the slower non-volatile memory into the volatile memory(often organized in a hierarchy) for execution by the processors of theelectronic device.

A network device (ND) is an electronic device that communicativelyinterconnects other electronic devices on the network (e.g., othernetwork devices, end-user devices). Some network devices are “multipleservices network devices” that provide support for multiple networkingfunctions (e.g., routing, bridging, switching, Layer 2 aggregation,session border control, Quality of Service, and/or subscribermanagement), and/or provide support for multiple application services(e.g., data, voice, and video). Network devices or network elements caninclude stations and access points in wireless communications systemssuch as wireless local area network (WLAN). Stations are devicesconnected to and communicating in a WLAN including client or userdevices that connect to the WLAN via access points. Access points arenetwork devices that may be specialized wireless access points that cancommunicate with other network devices in the WLAN via the wirelessmedium or via wired connections.

The IEEE 802.11 standard has limitations in the availability of thewireless medium and there have been various efforts to utilize moreaggressive mechanisms for improving wireless medium availability such asaltering the CCA threshold value or utilizing more aggressive CCAthresholds under defined conditions that improve the availability of thewireless medium and thereby increase system throughput. However,altering (e.g., increasing) the CCA threshold value may result in morefrequent packet collision and degradation of a Quality of Service (QoS)of the packet delivery. Especially, if a network device (e.g., a station(STA) or access point (AP)) assesses the wireless medium and a framethat occupies the wireless medium is to and/or from a network deviceunder the same basic service set (BSS) that the network device isassociated with. For example, in a case where the CCA threshold value isincreased and a STA initiates a transmission to a serving AP, thetransmission will not be successful because the AP is currently in themiddle of transmission/reception with another STA.

In one example, to prevent such cases while still altering the CCAthreshold scheme to improve wireless availability, the concept of aCOLOR subfield in physical layer header (more specifically in a SIGfield or more precisely the HE-SIG-A field) is proposed. The COLORsubfield indicates the BSS that the transmitter (or receiver) of theframe belongs to. The COLOR subfield may be smaller than a field thatwould be necessary for a full BSS to reduce the overhead in transmittingBSS information. Therefore, if COLOR information is provided in atransmitted frame, when a STA assesses the wireless medium andidentifies a start of a frame, the STA can further check the COLORsubfield and identify the BSS that the transmitter (or receiver) of theframe belongs to. If the COLOR subfield matches with the COLOR of theSTA's own BSS, then the STA will not initiate a transmission even if thereceived power level is below a CCA threshold.

In some implementations, to further improve the use of a COLOR subfield,the processes may define two CCA threshold values. In particular, afirst CCA threshold (Thr1) and a second CCA threshold (Thr2) may bedefined, such that the first CCA threshold value is equal to or lessthan the second CCA threshold value. If the received signal quality(e.g., received signal power) is lower than Thr1, the STA assesses thewireless medium to be “IDLE.” In contrast, if the received signalquality is higher than Thr2, the STA assesses the wireless medium to be“BUSY.” If the received signal quality is between Thr1 and Thr2, thenthe STA assesses the wireless medium status differently depending on theCOLOR information of the received frame. Here, if the COLOR subfieldmatches with that of the STA, then the STA assesses the wireless mediumto be “BUSY.” But if the COLOR subfield does not match with that of theSTA, then the STA assesses wireless medium to be “IDLE.” By doing so,the STA's effective CCA threshold is increased from Thr1 to Thr2 exceptfor the case that a frame that occupies the wireless medium belongs tothe same BSS.

The example of the use of multiple CCA threshold values and the use of aCOLOR subfield to distinguish between the CCA thresholds is provided byway of example and not limitation. One skilled in the art wouldunderstand that the process described herein would apply to othersimilar modifications to the CCA process that utilize multiple CCAthreshold values that require an examination of data in a receivedframe. In particular, the embodiments relate to the cases where theframe is received during a backoff period. As described further hereinbelow, a backoff is a time period that occurs after the completion of atransmission of a previous frame on a wireless medium. Typically, thebackoff occurs after an interframe space (IFS), such as an arbitrationIFS (AIFS). The IFS and backoff serve to ensure that sufficient time hasoccurred for the completion of a prior transmission and for a CCA to beperformed before a wireless medium is utilized again. The backoff periodcan have any length or duration and is implemented using a backoffcounter that starts at a particular value and counts down until itreaches zero at which time the implementing device can transmit assumingthat the wireless medium is IDLE. However, the introduction of thisexample more complex CCA process and similar CCA processes that evaluatethe content of the received frame introduce issues with the handling ofthe backoff counter.

Using the example of the above inspection of the COLOR subfield in thereceived frame, when a STA begins to assess the wireless medium, thebackoff counter value may be set at 6 (or any other suitable fixedvalue). When the STA is in the middle of assessing the wireless medium(i.e., after the completion of a prior transmission), the wirelessmedium becomes “IDLE” from “BUSY.” Then, the STA waits further for anAIFS time and as the wireless medium stays “IDLE” the STA startsdecreasing the backoff counter after the AIFS. In some cases, the STAmay receive another frame during the backoff. The backoff counter mayhave decreased to four ( ), at which point the STA identifies abeginning of a new frame, where the received signal quality of this newframe is between Thr1 and Thr2. With this received signal quality, theCCA decision relies on the COLOR subfield information. Thus, the STAneeds to further decode the preamble of the received frame to come to adecision on the status of the wireless medium. Because the initialdecision on the signal quality of the received frame is done at thestart of the frame, but COLOR subfield identification is done at a laterpart (after decoding at least part of preamble part), it is not clearhow to set the backoff counter value during this period. If the STAdecreases the backoff counter during this period, but the COLOR subfieldmatches, this results in decreasing the backoff counter when thewireless medium is “BUSY.” This is contrary to the standard use of thebackoff. However, if the STA stops decreasing the backoff counter duringthis period and the COLOR subfield doesn't match, this results in notdecreasing the backoff counter when the channel is “IDLE,” which is alsocontrary to the standard use of the backoff. Therefore, both casescreate new issues with how to handle the backoff counter during thedecoding of information in the received frame to determine the status ofthe wireless medium. The embodiments, described herein below, providemultiple processes for addressing this issue and for providing improveduse of the wireless medium by management of the backoff counter duringdecoding of the received frame.

FIG. 1 is a flowchart of one embodiment of a process for backoffadjustment. The embodiments provide a method and system for backoffadjustment. More specifically, a method that can calculate and adjustthe backoff counter depending on received signal quality and informationin the physical layer header of the received frame. In one embodiment,the process begins when a network device begins to assess a wirelessmedium. In particular the network device determines the end of an IFSand starts the operation of a backoff counter to track a backoff beforetransmitting a queued frame to be transmitted by the network device(Block 101). The network device decrements the backoff counter at anytimer interval (Block 103). If the network detects the start of a frameon the wireless medium (Block 105), then the process of determiningwhether the backoff counter is to be adjusted begins. If no signal isdetected on the wireless medium, then the process checks whether thebackoff counter has reached zero (Block 125) and if not continues todecrement the backoff counter (Block 103). If the backoff counterreaches zero (Block 125), then the network device can transmit on thewireless medium (Block 127). In some embodiments, the received signal isan orthogonal frequency division multiplexing (OFDM) signal of a frame.In some embodiments, when the frame is initially detected, the wirelessmedium can be assessed to be either IDLE or BUSY pending a finaldetermination.

In response to detecting a signal on the wireless medium, the networkdevice determines a status and how to adjust a backoff counter bychecking if the received frame has a signal quality that is greater thana first CCA threshold value (Block 107). If the signal quality exceedsthe first CCA threshold value, then the network device assesses thewireless medium as BUSY and stops decreasing the backoff counter (Block109). A signal quality can refer herein to any metric related to thesignal including signal power (e.g., received signal strength indicator(RSSI)), noise-to-signal ratio or similar measurement of the signalquality. If the received signal quality is above than a first CCAthreshold value then a check is made whether the signal quality isgreater than a second CCA threshold value, where the second CCAthreshold value is higher than the first CCA threshold value (Block111). If the signal quality was not above the first CCA threshold, thenthe medium is assessed as being IDLE (Block 109). The process thencontinues to decrease the backoff counter until it reaches zero (Block125). If the signal quality is above the second CCA threshold value,then the network device assesses the wireless medium as BUSY andmaintains the current counter value until a point that the wirelessmedium is no longer busy (Block 113).

If the signal quality is below than the second CCA threshold (but abovethe first CCA threshold), then the received signal quality is in betweenthe first CCA threshold value and the second CCA threshold value. Theprocess is illustrated to make the comparisons of the first CCAthreshold and second CCA threshold sequentially; however, one skilled inthe art would appreciate that these comparisons can be combined and/ordone in parallel. The network device then begins an adjustment of thebackoff counter (Block 115). The method of starting the process can varydependent on the embodiment of the process implemented. The backoffcounter can continue to be decremented or can be held at its currentvalue. After determining that the signal is below the second threshold,the backoff counter current value can be stored if it needs to berestored at a later point in the process. Once one of these initialactions is implemented the CCA assessment continues by decoding thepreamble of the received frame to complete the assessment of the stateof the wireless medium (Block 117). If the decoded physical layer (PHY)preamble indicates that the transmitter or receiver of the frame belongsto the same BSS as the network device (Block 119), then the CCAassessment determines that the wireless medium is BUSY (Block 121). Ifthe BSS of the received frame does not match the BSS of the networkdevice then the CCA assessment completes the backoff counter adjustment(Block 123). The decoding of the preamble may not directly lead toobtaining a full BSS, instead a shortened representation or similaridentifier, such a COLOR subfield, may be present in the preamble toidentify the BSS associated with the frame. In other embodiments, otherdata related to the determination of the evaluation of the availabilityof the wireless medium can be encoded in the preamble and handled withregard to the backoff adjustment in the same manner. The completion ofthe adjusted backoff counter process is dependent on the overall backoffcounter adjustment process and can include actions that are dependent onthe BSS or a similar data match. The actions can include holding adecrementing of the backoff counter until completion of the transmissionof the frame, the payload of the frame, the frame and an IFS, thepreamble or similar delay. The actions can include a continueddecrementing of the backoff counter, or can include a fixed valuedecrement such as subtracting a fixed value that roughly represents thedelay in processing the preamble information. Other actions can includerestoring a save backoff counter value. The complete examples andvariations on the actions taken during the start and completion of theadjusted back off counter process are described herein below withrelation to FIGS. 2-6B.

In some embodiments, the process described with regard to FIG. 1utilizes a combination of a CCA threshold and an overlapping BSS (OBSS)threshold. In this embodiment, the second CCA threshold is an OBSSthreshold (e.g., OBSS_PD threshold value). In this embodiment, theprocess detects that a power level of the received frame is above a CCAthreshold and below OBSS threshold, where the OBSS threshold representsa threshold value of the amount of interference from an OBSS STA that areceiving STA considers the wireless channel to be BUSY. The processthen determines, based on the decoded preamble that the BSS of thetransmitter of the received frame is from an OBSS in relation to a BSSof the network device. In response to determining that the BSS of thetransmitter of the frame is an OBSS in relation to the BSS of thenetwork device, the process indicates that the wireless medium is idle.Where the BSS of the transmitter of the received frame is the same or islikely the same as a BSS of the network device (i.e., the BSS isindicated in the COLOR field of the frame as a shortened identifier ofthe BSS identifier such that an association between COLOR value and BSSmay be established, but possibly not a direct/complete match), theprocess indicates that the wireless medium is busy.

In this embodiment, the process decrements a random backoff counterprior to the detection of the start of the frame, where a ‘random’backoff counter is a backoff counter that has a variable starting pointin its count down. The process may hold the random backoff counter upondetection of the start of the frame. The COLOR field in the preamble ofthe frame is decoded and then decrementing the random backoff counter isresumed after the decoding of the COLOR field of the frame completes,when the COLOR field of the frame matches a COLOR field of the networkdevice. In other embodiments, decrementing the random backoff counterafter decoding the COLOR field of the frame may resume when the COLORfield of the frame is different from a COLOR field of the networkdevice. As used herein, the backoff counters may be initiated withrandom values (within a range of possible values).

FIG. 2 is a diagram illustrating a CCA process according to oneembodiment, including a backoff counter process. The diagram illustratesthe timing of signals and the backoff counter in a CCA process. Afterthe wireless medium becomes free, an AIFS is observed before starting abackoff counter that will determine when the implementing network devicecan begin transmission. It is assumed in these embodiments and in thisexample that the network device has a frame queued to transmit and thusis monitoring the wireless medium using the CCA process to determinewhen the frame can be transmitted on the wireless medium.

After the AIFS completes, the network device initializes the backoffcounter at a configured value. In this example, the value of the backoffcounter is 6 and it begins decrementing. If it reached a value of 0,then the network device could transmit on the wireless medium. However,the other embodiments described herein provide a system and process forhandling adjusting the backoff counter in cases where there is anothersignal detected on the wireless medium. As discussed herein above, morecomplex CCA processes may involve multiple CCA thresholds and requirethe decoding of some of the preamble of received frames to complete adetermination of the state of the wireless medium. This leaves thequestion of how to handle the backoff counter during the time when thepreamble is being received and processed.

FIG. 3A is a diagram illustrating a first embodiment of an alternatebackoff counter process. Similar to the previous example of FIG. 2, inthis example when a network device begins to assess the wireless medium,the backoff counter value is set at 6. However, one skilled in the artwould understand that any value could be utilized consistent with theCCA process timing. When the wireless medium becomes IDLE, the networkdevice waits for a predetermined interframe space (IFS) time (in thisexample AIFS). While the wireless medium remains IDLE, the networkdecreases the backoff counter value after the end of the AIFS time. Inthis example, when the backoff counter reaches 3, the network deviceidentifies a beginning of a new frame, wherein the received power ofthis new frame is between the first CCA threshold value and the secondCCA threshold value.

In this embodiment, when the received signal quality is between thefirst CCA threshold and the second CCA threshold values, the networkdevice assesses the wireless medium as BUSY and stops decreasing thebackoff counter, at least until the network device checks information inthe physical layer (PHY) preamble. In this example, the relevant PHYpreamble includes a COLOR subfield, wherein the COLOR subfield indicatesthe BSS that the transmitter of the frame belong to, and the COLORsubfield matches or is associated with that of the BSS of the networkdevice. Since the COLOR subfield matches, the network device keeps thewireless medium assessment status as BUSY until the end of the frame.This scenario can happen in multiple different situations, such as i)the frame is a legacy frame that does not have the COLOR subfield, orii) the network device fails to successfully decode the physical layerpreamble.

FIG. 3B is a diagram illustrating a first embodiment of an alternatebackoff counter process. This illustrated example is the same as thatshown in FIG. 3A except that the information on the PHY preamble doesnot match with the COLOR (i.e., the BSS) of the network device. Thisscenario can happen in multiple different situations, such as the framecarries the COLOR subfield but the COLOR subfield in the frame does notmatch with that of the network device. Similar to the example shown inFIG. 3A, when the backoff counter was decreased to 3, the network deviceidentifies a beginning of a new frame, wherein the received signalquality of this new frame is between the first CCA threshold value andthe second CCA threshold value. As the received signal quality isbetween the first CCA threshold and the second CCA threshold values, thenetwork device assesses the wireless medium as BUSY and stops decreasingthe backoff counter at least until the network device checks theinformation in the PHY preamble. In this case, the COLOR subfieldinformation doesn't match the BSS of the network device, then thenetwork device changes the wireless medium assessment status to IDLE andresumes decreasing the backoff counter. When the backoff counterexpires, the network device initiates its own transmission.

FIG. 4A is a diagram illustrating an example of the second embodiment ofan alternate backoff counter process. Similar to the previous example ofthe first embodiment shown in FIG. 3A, in this example when a networkdevice begins to assess the wireless medium, the backoff counter valueis set at 6. When the wireless medium becomes IDLE, the network devicewaits for a predetermined IFS time (in this example AIFS). While thewireless medium remains IDLE, the network device starts decreasing thebackoff counter value after AIFS time. When the backoff counter isdecreased to 3, in this example, the network device identifies abeginning of a new frame, wherein the signal quality of this new frameis between the first CCA threshold value and the second CCA thresholdvalue. As the received signal quality is between the first CCA thresholdand the second CCA threshold values, the network device assesses thewireless medium to be IDLE and continues decreasing the backoff counterat least until the network device checks the PHY preamble. In thisexample, the PHY preamble includes a COLOR subfield, wherein the COLORsubfield indicates the BSS that the transmitter or receiver of the framebelong to, and using this information it can be determined whether theCOLOR subfield matches with that of the network device. If the COLORsubfield matches the BSS of the network device, then the network devicechanges the wireless medium assessment status to BUSY and stopsdecreasing the backoff counter until the end of the frame. After the endof the transmission of the frame and the subsequent IFS the backoffcounter resumes decreasing.

FIG. 4B is a diagram illustrating the second embodiment of an alternatebackoff counter process. In the illustration of FIG. 4B, the case wherethe COLOR subfield does not match the BSS of the implementing networkdevice. Where the received frame has a signal quality that is in betweenthe first CCA threshold value and the second CCA threshold value, thenthe network device assesses the wireless medium as IDLE and continuesdecreasing the backoff counter until it decodes the PHY preamble of theframe. If the decoded PHY preamble indicates that the transmitter of theframe belongs to a different BSS than the network device, the networkdevice continues to consider the wireless medium assessment status to beIDLE and continues decreasing the backoff counter. This embodiment(FIGS. 4A and 4B) is more aggressive than the first embodiment (FIGS. 3Aand 3B), but increases collision possibilities.

FIG. 5A is a diagram illustrating a third embodiment of an alternatebackoff counter process. In the third embodiment, the CCA processprogresses largely the same as with the first two embodiments (FIGS. 3Aand 3B and FIGS. 4A and 4B, respectively), however, if the signalquality of the received signal is in between the first CCA thresholdvalue and the second CCA threshold value, the network device assessesthe wireless medium as IDLE and continues decreasing the backoff counteruntil it decodes the PHY preamble. If the decoded physical layerpreamble indicates that the transmitter or receiver of the frame belongsto the same BSS as the implementing network device, then the networkdevice changes the wireless medium assessment status to BUSY and stopsdecreasing the backoff counter and the backoff counter value is adjustedto the value at the start of the frame. Otherwise, the network devicecontinues the wireless medium assessment status as IDLE and continuesdecreasing the backoff counter. In this example the PHY preambleincludes a COLOR subfield, wherein the COLOR subfield indicates the BSSthat the transmitter or receiver of the frame belong to, and can be usedto determine whether the COLOR subfield matches with that of the networkdevice. In this case, the COLOR subfield matches, the network devicechanges the wireless medium assessment status to BUSY and stopsdecreasing the backoff counter until the end of the frame and thebackoff value is adjusted to 3 which is the value at the start of theframe. Therefore, when the network invokes the new backoff adjustment,after wireless medium becomes IDLE again, after waiting for AIFSduration, the STA decreases the backoff counter from the value of 3.Thus, in this embodiment, the value of the backoff counter may be storedat the start of the received frame, such that the value can be restored.In the example, the first value overlapping with the received frame,which could be stored to be used in case the COLOR subfield matched.This scenario can happen in multiple different situations such as i) theframe is a legacy frame that it does not have COLOR subfield, or ii) theSTA fails to successfully decode the physical layer preamble.

FIG. 5B is a diagram illustrating the third embodiment of an alternatebackoff counter process. This example is the same with the one shown inFIG. 5A except that the information on the physical layer preamble doesnot match with the COLOR of the STA. This scenario can happen inmultiple different situations such as the frame carries COLOR subfieldbut the COLOR subfield in the frame does not match with that of the STA.Similar to the example shown in FIG. 6, when the backoff counter wasdecreased to 4, the STA identifies a beginning of a new frame, whereinthe received power of this new frame is between the first CCA thresholdvalue and the second CCA threshold value. As the received signal levelis between the first and the second CCA threshold values, the STAassesses wireless medium as IDLE and continues decreasing the backoffcounter at least until the STA checks follow up information in thephysical layer preamble part. And as the COLOR subfield informationdoesn't match, the STA keeps wireless medium assessment status IDLE andcontinues decreasing the backoff counter. And, when the backoff counterexpires, the STA initiates its own transmission.

FIGS. 6A and 6B are diagrams illustrating a fourth embodiment of analternate backoff counter process. As the fourth embodiment can manage abackoff counter efficiently, it can have multiple benefits. The fourthembodiment encompasses a combination of some additional strategies forbackoff counter adjustment that can be used in combination with aspectsof the preceding embodiments. Thus, reference is also made toillustrations utilized in prior embodiments.

The fourth embodiment can handle a backoff mechanism efficiently even ina case where a frame occupying the wireless medium does not support aCOLOR subfield. The benefits of the fourth embodiment further includesmaintaining the backoff counter value correctly such that it canmaintain fairness among multiple network devices operating in a WLAN.This embodiment, does not require any significant change from aconventional backoff mechanism, therefore implementation complexity canbe minimized. The embodiment can avoid any ambiguity in backoff countermanagement from the start of the frame to the time the network devicedecodes the PHY preamble.

Throughout this fourth embodiment, CCA based on signal detection(CCA-SD) in primary channel is considered by way of example only. Forthose operations combined together with other mechanisms such as CCAbased on energy detection (CCA-ED) or CCA based on signaling detectionfor wider bandwidth which includes secondary channel can be applied incombination or in place of the CCA-SD in this example embodiment. In theillustrated example, when a network device is assessing a wirelessmedium, if the network device detects a start of signal or frame (e.g.,an OFDM frame) and if the received signal quality (e.g., sensitivitylevel) is above the first CCA threshold level Thr1, the network deviceassesses the medium as BUSY and the backoff slot boundary shall nothappen before the medium becomes IDLE again. If the received signalquality is below the second CCA threshold level Thr2, wherein Thr2 islower than Thr1, the network device assesses the medium as IDLE and thenetwork device may decrease the backoff counter value at the next slotboundary. If the network device detects a start of a frame and if thereceived signal quality is between Thr1 and Thr2, then the networkdevice may put the backoff counter on hold, which implies that a process(e.g., an Enhanced Distributed Channel Access Function (EDCAF)) thatcontrols the backoff counter does nothing at a coming slot boundary,while CCA status is still IDLE. Then, after checking the PHY preamblethat includes the COLOR subfield information, the network device (e.g.,via the EDCAF) releases the backoff on hold. When the backoff on hold isreleased depending on the COLOR subfield information, the network mayimplement one of a set of different actions.

If there is an event that changes CCA status decision from the first CCAthreshold status (e.g., IDLE) to the second CCA threshold status (e.g.,BUSY), such that the COLOR subfield information in the received framematches with that of the network, as the CCA becomes BUSY, the backoffcounter shall not be decreased until the wireless medium becomes IDLEagain. If there's no event that changes the CCA status decision, as thechannel assessment remains IDLE, the process shall keep decreasing thebackoff counter. If the backoff counter for that process has a nonzerovalue at the next slot boundary. (In some embodiments, the amount ofdecrement in the backoff counter value may be greater than 1 tocompensate for the elapsed time for the backoff on hold duration.) Theillustrated examples, a network device has a buffered data frame tosend, and thus, the process of the network device initiates atransmission procedure. After the medium becomes IDLE from BUSY state,the network device waits for AIFS time to elapse for a given accesscategory and as the medium remains IDLE during this time and further,the network device decreases backoff counter at each slot boundary.While the network device decreases the backoff counter a frame isdetected, in this example, when the backoff counter value reaches at 4.The received frame is sent from a 3^(rd) party STA or similar source.

Referring back to FIG. 3A, this illustration can also demonstrate a casewhere the received signal quality (e.g., sensitivity level (P_rx)) forthe frame on the medium is higher than the first threshold level (Thr1).As the received signal quality is higher than Thr1, the network deviceassesses the medium as being BUSY, and the backoff counter is notdecreased at least at until the end of the ongoing frame. After theongoing frame is finished and the medium becomes IDLE, and assuming theSTA decoded the payload of the ongoing frame correctly, the STA willstart to decrease the backoff counter after waiting for another AIFStime.

In reference to FIG. 4B, in combination with the above case, a case isshown where the received signal quality (e.g., sensitivity level) forthe received frame on the medium is lower than the second thresholdlevel Thr2. As the received signal quality is lower than Thr2, thenetwork device keeps the medium assessment as IDLE. Therefore, even inthe middle of the frame duration on the medium, the network devicedecreases the backoff counter value at each slot boundary. When thebackoff counter expires, the backoff counter transmits the data frame.

In reference to FIG. 3B, a case is shown that the received signalquality for the frame on the medium is between Thr1 and Thr2, and theCOLOR subfield information of the frame on the medium does not matchwith that of the STA. As the received signal quality is between Thr1 andThr2, the STA puts the backoff counter on hold while maintaining thechannel assessment as IDLE. Therefore, there's no change in the backoffcounter until the backoff on hold is released. When the process decodesthe preamble part that comprises the COLOR subfield, the network devicereleases the backoff that was on hold. As the STA identifies that theCOLOR subfield does not match with that of the network device andthere's no activities that change the channel assessment decision, thenetwork device resumes decreasing the backoff counter from the next slotboundary, which may come even in the middle of the current frame on themedium. And, the network device transmits the data frame when thebackoff counter expires. In this case, when the backoff that was on holdis released, the STA decreases the backoff counter value by one at thenext slot boundary.

In reference to FIG. 6A, a case is shown that the received signalquality for the frame on the medium is between Thr1 and Thr2, and theCOLOR subfield information of the frame on the medium does not matchwith that of the network device. As the received signal quality isbetween Thr1 and Thr2, the network device puts the backoff counter onhold while maintaining the channel assessment as IDLE. Therefore,there's no change in backoff counter until the backoff on hold isreleased. When the network device decodes the preamble part thatcomprises the COLOR subfield, the network device releases the backoffthat was on hold. As the network device identifies that the COLORsubfield does not match with that of the network device and there's noactivities that changes the channel assessment decision, the networkdevice resumes decreasing the backoff counter from the next slotboundary, which may come even in the middle of the current frame on themedium. And, the network device transmits the data frame when thebackoff counter expires. In this case, when the backoff that was on holdis released, the network device decreases the backoff counter value bygreater than or equal to one at the next slot boundary that compensatesfor the duration that backoff was on hold. In this example, the backoffcounter was decreased from 4 to 1.

Referring again to FIG. 3A, a case is shown that the received signalquality for the frame on the medium is between Thr1 and Thr2, and theCOLOR subfield information of the frame on the medium matches with thatof the network device. As the received signal quality is between Thr1and Thr2, the network device puts the backoff counter on hold whilemaintaining the channel assessment as IDLE. Therefore, there's no changein backoff counter until the backoff on hold is released. When the STAdecodes the preamble part that comprises the COLOR subfield, the STAreleases the backoff that was on hold. As the STA identifies that theCOLOR subfield matches with that of the STA and there's activity thatchanges the channel assessment decision from idle to busy, the STA stopsdecreasing the backoff counter at least until the channel assessmentresults becomes idle again. After the ongoing frame is finished and themedium becomes idle, and assuming the STA decoded the payload of theongoing frame correctly, the network device will start to decrease thebackoff counter after waiting for another AIFS time. In this case, thenetwork device decreases the backoff counter value by one at the nextslot boundary.

In reference to FIG. 6B, another case is shown that the received signalquality for the frame on the medium is between Thr1 and Thr2, and theCOLOR subfield information of the frame on the medium matches with thatof the network device. As the received signal quality is between Thr1and Thr2, the network device puts the backoff counter on hold whilemaintaining the channel assessment as idle. Therefore, there's no changein backoff counter until the backoff on hold is released. When thenetwork device decodes the preamble part that comprises the COLORsubfield, the network device releases the backoff that was on hold. Asthe network device identifies that the COLOR subfield matches with thatof the network device and there's activity that changes the channelassessment decision from idle to busy, the network device stopsdecreasing the backoff counter at least until the channel assessmentresults becomes idle again. After the ongoing frame is finished and themedium becomes idle, and assuming the network device decoded the payloadof the ongoing frame correctly, the network will start to decrease thebackoff counter after waiting for another AIFS time. In this case, whenthe backoff that was on hold is released, the network device decreasesthe backoff counter value by greater than or equal to one at the nextslot boundary that compensates for the duration that backoff was onhold. In this example, the backoff counter was decreased from 4 to 1.

Thus the embodiments disclosed herein above have been shown such thatthey can be implemented in various different ways and combinations, allwithout departing from the spirit or scope of the present invention.

FIG. 7 is a diagram of a network device implementing a station or accesspoint that executes a backoff counter adjustment process and module. Ina wireless local area network (WLAN) such as the example WLANillustrated in FIG. 10, a basic service set (BSS) includes a pluralityof network devices referred to herein as WLAN devices. Each of the WLANdevices may include a medium access control (MAC) layer and a physical(PHY) layer according to IEEE (Institute of Electrical and ElectronicsEngineers) 802.11 standard. In the plurality of WLAN devices, at leastone WLAN device may be an access point (AP) station (e.g., access point0 and access point 1 in FIG. 13) and the other WLAN devices may benon-AP stations (non-AP STAs), (e.g., stations 0-3 in FIG. 13).Alternatively, all of the plurality of WLAN devices may be non-AP STAsin an Ad-hoc networking environment. In general, the AP STA and thenon-AP STA may be each referred to herein as a station (STA). However,for ease of description, only the non-AP STA will be referred to hereinas a STA whereas the AP stations are referred to herein as APs for easeof description. As shown in FIG. 10, a WLAN can have any combination ofstations and access points that can form a discrete network, an ad hocnetwork or any combination thereof. Any number of APs and stations canbe included in a WLAN and any topology and configuration of such APs andstations in the network can be utilized.

Referring to FIG. 7, the example WLAN device 1 includes a basebandprocessor 10, a radio frequency (RF) transceiver 20, an antenna unit 30,memory 40, an input interface unit 50, an output interface unit 60, anda bus 70. The baseband processor 10 performs baseband signal processing,and includes a MAC processor 11 and a PHY processor 15. These processorscan be any type of integrated circuit (IC) including a generalprocessing unit or an application specific integrated circuit (ASIC).

In one embodiment, the MAC processor 11 may include a MAC softwareprocessing unit 12 and a MAC hardware processing unit 13. The memory 40may store software (hereinafter referred to as “MAC software”),including at least some functions of the MAC layer. The MAC softwareprocessing unit 12 executes the MAC software to implement some functionsof the MAC layer and the MAC hardware processing unit 13 may implementthe remaining functions of the MAC layer in hardware (hereinafterreferred to “MAC hardware”). However, the MAC processor 11 is notlimited to this distribution of functionality.

The PHY processor 15 includes a transmitting signal processing unit 100and a receiving signal processing unit 200 described further hereinbelow with reference to FIGS. 11 and 12. In some embodiments, the PHYprocessor 15 can also implement an enhanced CCA module 300 and/or thebackoff counter adjustment module 400. The enhanced CCA module 300 andthe backoff counter adjustment module 400 can implement the respectivefunctions for any combination of the embodiments described herein abovewith regard to FIGS. 1-6B. In other embodiments, these modules may beimplemented by or distributed over both the PHY processor 15 and the MACprocessor 11. These modules may be implemented as software or ashardware components of either the PHY processor 15 or MAC processor 11.These modules can be implemented as components of the transmittingsignal processing unit 100 and the receiving signal processing unit 200or as discrete components. In a further embodiment, the enhanced CCAmodule 300 and/or the backoff adjustment module 400 can be implementedby separate components or processors within the baseband processor.

The baseband processor 10, the memory 40, the input interface unit 50,and the output interface unit 60 may communicate with each other via thebus 70. The radio frequency (RF) transceiver 20 includes an RFtransmitter 21 and an RF receiver 22. The memory 40 may further store anoperating system and applications. In some embodiments, the memory maystore the nearby stations set. The input interface unit 50 receivesinformation from a user and the output interface unit 60 outputsinformation to the user.

The antenna unit 30 includes one or more antennas. When a multiple-inputmultiple-output (MIMO) or a multi-user MIMO (MU-MIMO) system is used,the antenna unit 30 may include a plurality of antennas.

FIG. 8 is a schematic block diagram exemplifying a transmitting signalprocessor in a WLAN device. Referring to the above drawing, atransmitting signal processing unit 100 includes an encoder 110, aninterleaver 120, a mapper 130, an inverse Fourier transformer (IFT) 140,and a guard interval (GI) inserter 150. The encoder 110 encodes inputdata. For example, the encoder 110 may be a forward error correction(FEC) encoder. The FEC encoder may include a binary convolutional code(BCC) encoder followed by a puncturing device or may include alow-density parity-check (LDPC) encoder.

The transmitting signal processing unit 100 may further include ascrambler for scrambling the input data before encoding to reduce theprobability of long sequences of 0s or 1s. If BCC encoding is used inthe encoder 110, the transmitting signal processing unit 100 may furtherinclude an encoder parser for demultiplexing the scrambled bits among aplurality of BCC encoders. If LDPC encoding is used in the encoder 110,the transmitting signal processing unit 100 may not use the encoderparser.

The interleaver 120 interleaves the bits of each stream output from theencoder to change the order of bits. Interleaving may be applied onlywhen BCC encoding is used. The mapper 130 maps the sequence of bitsoutput from the interleaver to constellation points. If LDPC encoding isused in the encoder 110, the mapper 130 may further perform LDPC tonemapping in addition to constellation mapping.

When multiple input-multiple output (MIMO) or multiple user (MU)-MIMO isused, the transmitting signal processing unit 100 may use a plurality ofinterleavers 120 and a plurality of mappers 130 corresponding to thenumber N_(SS) of spatial streams. In this case, the transmitting signalprocessing unit 100 may further include a stream parser for dividingoutputs of the BCC encoders or the LDPC encoder into blocks that aresent to different interleavers 120 or mappers 130. The transmittingsignal processing unit 100 may further include a space-time block code(STBC) encoder for spreading the constellation points from the N_(SS)spatial streams into N_(STS) space-time streams and a spatial mapper formapping the space-time streams to transmit chains. The spatial mappermay use direct mapping, spatial expansion, or beamforming.

The IFT 140 converts a block of the constellation points output from themapper 130 or the spatial mapper to a time domain block (i.e., a symbol)by using an inverse discrete Fourier transform (IDFT) or an inverse fastFourier transform (IFFT). If the STBC encoder and the spatial mapper areused, the inverse Fourier transformer 140 may be provided for eachtransmit chain.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may insert cyclic shift diversities (CSDs) to prevent unintentionalbeamforming. The CSD insertion may occur before or after the inverseFourier transform 140. The CSD may be specified per transmit chain ormay be specified per space-time stream. Alternatively, the CSD may beapplied as a part of the spatial mapper. When MU-MIMO is used, someblocks before the spatial mapper may be provided for each user.

The GI inserter 150 prepends a GI to the symbol. The transmitting signalprocessing unit 100 may optionally perform windowing to smooth edges ofeach symbol after inserting the GI. The RF transmitter 21 converts thesymbols into an RF signal and transmits the RF signal via the antennaunit 30. When MIMO or MU-MIMO is used, the GI inserter 150 and the RFtransmitter 21 may be provided for each transmit chain.

FIG. 9 a schematic block diagram exemplifying a receiving signalprocessing unit in the WLAN. Referring to FIG. 9, a receiving signalprocessing unit 200 includes a GI remover 220, a Fourier transformer(FT) 230, a demapper 240, a deinterleaver 250, and a decoder 260.

An RF receiver 22 receives an RF signal via the antenna unit 30 andconverts the RF signal into symbols. The GI remover 220 removes the GIfrom the symbol. When MIMO or MU-MIMO is used, the RF receiver 22 andthe GI remover 220 may be provided for each receive chain.

The FT 230 converts the symbol (i.e., the time domain block) into ablock of constellation points by using a discrete Fourier transform(DFT) or a fast Fourier transform (FFT). The Fourier transformer 230 maybe provided for each receive chain.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use a spatial demapper for converting the Fourier transformedreceiver chains to constellation points of the space-time streams and anSTBC decoder for despreading the constellation points from thespace-time streams into the spatial streams.

The demapper 240 demaps the constellation points output from the Fouriertransformer 230 or the STBC decoder to bit streams. If LDPC encoding isused, the demapper 240 may further perform LDPC tone demapping beforeconstellation demapping. The deinterleaver 250 deinterleaves the bits ofeach stream output from the demapper 240. Deinterleaving may be appliedonly when BCC encoding is used.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use a plurality of demappers 240 and a plurality of deinterleavers250 corresponding to the number of spatial streams. In this case, thereceiving signal processing unit 200 may further include a streamdeparser for combining the streams output from the deinterleavers 250.

The decoder 260 decodes the streams output from the deinterleaver 250 orthe stream deparser. For example, the decoder 100 may be an FEC decoder.The FEC decoder may include a BCC decoder or an LDPC decoder. Thereceiving signal processing unit 200 may further include a descramblerfor descrambling the decoded data. If BCC decoding is used in thedecoder 260, the receiving signal processing unit 200 may furtherinclude an encoder deparser for multiplexing the data decoded by aplurality of BCC decoders. If LDPC decoding is used in the decoder 260,the receiving signal processing unit 100 may not use the encoderdeparser.

A frame as used herein may refer to a data frame, a control frame, or amanagement frame may be exchanged between WLAN devices. The data frameis used for transmission of data forwarded to a higher layer. The WLANdevice transmits the data frame when the wireless medium is consideredto be in an idle condition or state such as after performing backoff ifa DIFS has elapsed from a time when the medium was not busy or undersimilar conditions. The management frame is used for exchangingmanagement information, which is not forwarded to the higher layer.Subtype frames of the management frame include a beacon frame, anassociation request/response frame, a probe request/response frame, andan authentication request/response frame. The control frame is used forcontrolling access to the medium. Subtype frames of the control frameinclude a request to send (RTS) frame, a clear to send (CTS) frame, andan acknowledgement (ACK) frame. In the case that the control frame isnot a response frame of the other frame, the WLAN device transmits thecontrol frame after performing backoff if the DIFS has elapsed. In thecase that the control frame is the response frame of the other frame,the WLAN device transmits the control frame without performing backoffif a short IFS (SIFS) has elapsed. The type and subtype of frame may beidentified by a type field and a subtype field in a frame control field.

On the other hand, a Quality of Service (QoS) STA may transmit the frameafter performing backoff if an arbitration IFS (AIFS) for an associatedaccess category (AC), i.e., AIFS[AC] has elapsed. In this case, the dataframe, the management frame, or the control frame, which is not theresponse frame, may use the AIFS[AC].

As discussed herein CCA and in particular an enhanced CCA module isimplemented to manage the transmission of frames by the WLAN device. CCAmay implement a CSMA (carrier sense multiple access)/CA (collisionavoidance) based frame transmission procedure or similar procedure foravoiding collisions between frames in a channel. The backoff adjustmentmodule is implemented to adjust the backoff counter to take intoconsideration the complexities of the enhanced CCA module functioningthat may require that some decoding of the PHY preamble take placebefore a decision can be made about the status of the wireless medium

FIG. 11 is a timing diagram providing an example of the CSMA/CAtransmission procedure. In the illustrated example, STA1 is a transmitWLAN device for transmitting data, STA2 is a receive WLAN device forreceiving the data, and STA3 is a WLAN device, which may be located atan area where a frame transmitted from the STA1 and/or a frametransmitted from the STA2 can be received by the WLAN device.

STA1 may determine whether the channel is busy by carrier sensing. TheSTA1 may determine the channel occupation based on a quality of thesignal on the channel or correlation of signals in the channel, or maydetermine the channel occupation by using a network allocation vector(NAV) timer.

When determining that the channel is not used by other devices duringDIFS (that is, the channel is idle), STA1 may transmit an RTS frame toSTA2 after performing backoff. Upon receiving the RTS frame, STA2 maytransmit a CTS frame as a response of the CTS frame after SIFS. WhenSTA3 receives the RTS frame, it may set the NAV timer for a transmissionduration of subsequently transmitted frames (for example, a duration ofSIFS+CTS frame duration+SIFS+data frame duration+SIFS+ACK frameduration) by using duration information included in the RTS frame. WhenSTA3 receives the CTS frame, it may set the NAV timer for a transmissionduration of subsequently transmitted frames (for example, a duration ofSIFS+data frame duration+SIFS+ACK frame duration) by using durationinformation included in the RTS frame. Upon receiving a new frame beforethe NAV timer expires, STA3 may update the NAV timer by using durationinformation included in the new frame. STA3 does not attempt to accessthe channel until the NAV timer expires.

When STA1 receives the CTS frame from the STA2, it may transmit a dataframe to the STA2 after SIFS elapses from a time when the CTS frame hasbeen completely received. Upon successfully receiving the data frame,the STA2 may transmit an ACK frame as a response of the data frame afterSIFS elapses.

When the NAV timer expires, STA3 may determine whether the channel isbusy through the use of carrier sensing techniques. Upon determiningthat the channel is not used by other devices during DIFS and after theNAV timer has expired, STA3 may attempt channel access after acontention window according to random backoff elapses.

The solutions provided herein have been described with reference to awireless LAN system; however, it should be understood that thesesolutions are also applicable to other network environments, such ascellular telecommunication networks, wired networks, and similarcommunication networks.

An embodiment of the invention may be an article of manufacture in whicha non-transitory machine-readable medium (such as microelectronicmemory) has stored thereon instructions which program one or more dataprocessing components (generically referred to here as a “processor”) toperform the operations described above. In other embodiments, some ofthese operations might be performed by specific hardware components thatcontain hardwired logic (e.g., dedicated digital filter blocks and statemachines). Those operations might alternatively be performed by anycombination of programmed data processing components and fixed hardwiredcircuit components.

The PHY entity for 802.11 implemented in the WLAN device is based onorthogonal frequency division multiple access OFDM or OFDMA. In eitherOFDM or OFDMA PHY layers, a STA is capable of transmitting and receivingPPDUs that are compliant with the mandatory PHY specifications. In a PHYspecification, set of MCS and maximum number of spatial streams aredefined. Also in some PHY entities, downlink and/or uplink MUtransmission with a maximum number of space-time streams per user and upto a fix total number of space-time streams is defined.

FIG. 12 is a diagram of a very high throughput (VHT) PPDU utilized bythe WLAN device PHY layer. FIG. 13 is a table of the fields of the VHTPPDU. Some PHY entities define PPDU that are individually addressed(where identification is based on AID or Partial AID) and some are groupaddressed (where identification is based on Group ID, GID). Some PHYentities provide support for 20 MHz, 40 MHz, 80 MHz and 160 MHzcontiguous channel widths and support for 80+80 MHz non-contiguouschannel width. The data subcarriers are modulated using binary phaseshift keying (BPSK), quadrature phase shift keying (QPSK), 16-quadratureamplitude modulation (16-QAM), 64-QAM and 256-QAM. Forward errorcorrection (FEC) coding (convolutional or LDPC coding) is used withcoding rates of 1/2, 2/3, 3/4 and 5/6.

In each PHY entity, there would be fields denoted as L-SIG, SGI-A, SIG-Bwhere some crucial information about the PSDU attributes are listed.These symbols are usually encoded with the most robust MCS. The L-SIG,SGI-A, SIG-B have very limited number of bits and it is desired toencode them in the most compact form possible. In a receiving STA, firstthese symbols are decoded in order to obtain vital information about thePSDU attributes and some MAC attributes. In IEEE 802.11 ac, thesesymbols are called VHT SIG-A and VHT SIG-B symbols.

As discussed above, WLAN devices are currently being deployed in diverseenvironments. These environments are characterized by the existence ofmany access points and non-AP stations in geographically limited areas.Increased interference from neighboring devices gives rise toperformance degradation. Additionally WLAN devices are increasinglyrequired to support a variety of applications such as video, cloudaccess, and offloading. In particular video traffic is expected to bethe dominant type of traffic in many high efficiency WLAN deployments.With the real-time requirements of some of these applications, WLANusers demand improved performance in delivering their applications,including improved power consumption for battery-operated devices.

IEEE 802.11 ax or HE SIG-A and IEEE 802.11 ax or HE SIG-B are referredto simply as simply by SIG-A and SIG-B and are amendments to the 802.11standard directed at addressing these problems. Unlike previousamendments where the focus was on improving aggregate throughput, thisamendment focuses on improving metrics that reflect user experience,such as average per station throughput, the 5th percentile of perstation throughput of a group of stations, and area throughput.Improvements will be made to support environments such as wirelesscorporate office, outdoor hotspot, dense residential apartments, andstadiums.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in conferencingtechnology to most effectively convey the substance of their work toothers skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. It should be borne in mind,however, that all of these and similar terms are to be associated withthe appropriate physical quantities and are merely convenient labelsapplied to these quantities. Unless specifically stated otherwise asapparent from the above discussion, it is appreciated that throughoutthe description, discussions utilizing terms such as those set forth inthe claims below, refer to the action and processes of a conferencedevice, or similar electronic computing device, that manipulates andtransforms data represented as physical (electronic) quantities withinthe conference device's registers and memories into other data similarlyrepresented as physical quantities within the conference device'smemories or registers or other such information storage, transmission ordisplay devices. Note the operations of the flowcharts are describedwith reference to the exemplary embodiments of the diagrams. However, itshould be understood that the operations of flowcharts can be performedby embodiments of the invention other than those discussed, and theembodiments of the diagrams can perform operations different than thosediscussed with reference to the flowcharts.

What is claimed is:
 1. A method implemented by a network device, themethod to improve efficiency for clear channel assessment (CCA) in awireless local area network (WLAN) by adjusting a backoff counter tominimize delay caused by decoding a preamble of a received signal, themethod comprising: detecting, on a wireless medium, a start of a frame;decoding a preamble of the frame to determine a basic service set (BSS)associated with a transmitter of the frame; indicating that the wirelessmedium is busy while decoding the preamble of the frame; decrementing arandom backoff counter prior to the detection of the start of the frame;holding the random backoff counter upon detection of the start of theframe; decoding a COLOR field in the preamble of the frame, the COLORfield is associated with the BSS; and resuming decrementing the randombackoff counter after decoding the COLOR field of the frame, when theCOLOR field of the frame is different from a COLOR field of the networkdevice.
 2. The method of claim 1, wherein the BSS is represented in theCOLOR field located in the preamble of the frame, wherein the wirelessmedium is indicated as busy until the COLOR field is decoded.
 3. Themethod of claim 2, further comprising: detecting that a power level ofthe frame is above a CCA threshold and below an overlapping BSS (OBSS)threshold; determining, based on the decoded preamble, that the BSS ofthe transmitter of the frame is an OBSS in relation to a BSS of thenetwork device; and indicating, in response to determining that the BSSof the transmitter of the frame is an OBSS in relation to the BSS of thenetwork device, that the wireless medium is idle.
 4. The method of claim2, further comprising: detecting that a power level of the frame isabove a CCA threshold and below an overlapping BSS (OBSS) threshold;determining, based on the decoded preamble, that the BSS of thetransmitter of the frame is the same as a BSS of the network device; andindicating, in response to determining that the BSS of the transmitterof the frame is the same as a BSS of the network device, that thewireless medium is busy.
 5. The method of claim 1, wherein the BSS isrepresented in the COLOR field located in the preamble of the frame,wherein the wireless medium is indicated as busy until the BSS of thetransmitter of the frame is determined based on the decoded COLOR field.6. A network device configured to implement a method to improveefficiency for clear channel assessment (CCA) in a wireless local areanetwork (WLAN) by adjusting a backoff counter to minimize delay causedby decoding a preamble of a received signal, the method comprising: aphysical processor to implement physical layer data processing; and anenhanced CCA module coupled to the physical processor, the enhanced CCAmodule configured to detect, on a wireless medium, a start of a frame,to decode a preamble of the frame to determine a basic service set (BSS)associated with a transmitter of the frame, to indicate that thewireless medium is busy while decoding the preamble of the frame, todecrement a random backoff counter prior to the detection of the startof the frame, to hold the random backoff counter upon detection of thestart of the frame, decode a COLOR field in the preamble of the frame,the COLOR field is associated with the BSS, and resume decrementing therandom backoff counter after decoding the COLOR field of the frame, whenthe COLOR field of the frame is different from a COLOR field of thenetwork device.
 7. The network device of claim 6, wherein the BSS isrepresented in the COLOR field located in the preamble of the frame,wherein the wireless medium is indicated as busy until the COLOR fieldis decoded.
 8. The network device of claim 7, wherein the enhanced CCAmodule is further configured to detect that a power level of the frameis above a CCA threshold and below an overlapping BSS (OBSS) threshold,to determine, based on the decoded preamble, that the BSS of thetransmitter of the frame is an OBSS in relation to a BSS of the networkdevice, and to indicate, in response to determining that the BSS of thetransmitter of the frame is an OBSS in relation to the BSS of thenetwork device, that the wireless medium is idle.
 9. The network deviceof claim 6, wherein the BSS is represented in the COLOR field located inthe preamble of the frame, wherein the wireless medium is indicated asbusy until the BSS of the transmitter of the frame is determined basedon the decoded COLOR field.